Universal Mobile Telecommunications System (UMTS) is a third-generation (3G) cell phone technology. Evolved-UMTS Terrestrial Radio Access (E-UTRA), also known as UMTS Long Term Evolution (3GPP LTE), is a key 3G technology to ensure the competitiveness of UMTS and provide a high-data-rate, low-latency and packet-optimized system. Unlike UMTS, which uses code division multiple access (CDMA) as the air interface, E-UTRA uses orthogonal frequency division multiplexing (OFDM) as the air interface.
In an OFDM cellular network, each cell employs a base station (ES) that communicates with any user equipment (UE), such as cell phones, laptop computers, or personal digital assistant (PDAs), active within its cell. When UE is first activated, it performs an initial cell search to connect to the cellular network. The initial cell search includes a downlink (DL) synchronization process between the BS and the UE in which the BS sends a synchronization signal to the UE.
After DL synchronization, the BS sends control information to the UE that the UE then uses to decode subsequent frames and sub-frames of data received from the BS. The UE must reliably receive the control information for the UE to be able to decode subsequently received data accurately. To guarantee fast and reliable receipt of control information, OFDM systems designate a fixed number of tones for transmitting the control information. Consequently, today's OFDM systems perform reliably and are capable of transmitting data at very high rates.